So-called heddle shafts are used for shedding in power looms. The heddle shafts are formed by a frame that is essentially rectangular in a front elevation view and whose upper and lower long, longitudinal edges are each formed by one shaft rod. Laterally, the shaft rods are joined by lateral bracing posts. The shaft rods are often formed by hollow chamber profiles. Heddle support rails that support the heddles are secured to the shaft rods. Each heddle has at least one yarn eyelet, through which a warp thread is guided. For shedding, the heddle shafts are moved up and down in rapid succession. For wide weaving widths, the result is very long shaft rods, which tend to sagging, as a function of the weaving speed (number of revolutions). To reduce such sagging and above all to avoid different sagging of different shaft rods, besides the lateral bracing posts, center connectors are occasionally used to join the shaft rods together. Such center connectors are struts that with their ends join the two shaft rods.
For instance, a heddle shaft with this kind of center connector is known from German Published, Examined Patent Disclosure DE-AS 26 20 778. The shaft rod comprises sheet-metal profiles, with a filler core between them, for instance of hard plastic foam, honeycomblike material, or a lightweight type of wood. The filler material is glued to the sheet-metal profiles. In order also to create a possible way of inserting the center connector, a free space between the sheet-metal profiles is filled with a rubber body, which is joined in firmly adhering fashion, for instance glued, to the flat sheet-metal profiles. An extension of a profile rail is retained in the rubber body, and with a widened head, this extension retains a so-called slide element that is also thrust into the interstice between the two sheet-metal profiles. Screws are inserted into this slide element and hold the center connector, here called an intermediate strut.
From Swiss Patent CH 547 366, a heddle shaft with an adjustable center connector is also known. Here the heddle shaft is formed by a hollow chamber profile, which in the region of the center connector may have a window oriented toward the respective other shaft rod. A retaining piece is disposed in the interior of the hollow chamber profile and is joined to the side walls of the hollow chamber profile.
This arrangement is not optimized for maximum weaving speeds.
From German Patent DE 32 20 710 C2, a heddle shaft is known with shaft rods which each, on their respective side toward the heddle support rail, have a narrow chamber for receiving a clamping piece. The chamber is accessible toward the heddle support rail through a window. A clamping piece inserted into the chamber acts here as an abutment for the center connector.
The transmission of force between the center connector and the shaft rod takes place in a relatively small space. Moreover, the embodiment of a longitudinally continuous chamber for the clamping piece requires increased consumption of material and thus results in a considerable mass for the shaft rod.
A shaft rod also embodied as a hollow profile is found in German Patent DBP 1083759. For attaching a plurality of center connectors, each shaft rod is provided, on its opening toward the heddle support rail, with an opening through which a suitable retaining piece disposed in the interior is accessible. The retaining piece has threaded bores for receiving screws, which retain the center connector.
With this as the point of departure, it is the object of the invention to create a heddle shaft which is especially suitable for high-speed power looms.